1. Field of the Invention
The invention generally relates to a rotation direction control method for a cooling fan and a rotation direction control circuit thereof; more particularly, to a rotation direction control method, that adjusts output rotation commands thereof based on a detected temperature, and a rotation direction control circuit thereof.
2. Description of the Related Art
Cooling fans are often installed in electronic devices for heat dissipation. During the operation of a cooling fan, the cooling fan rotates in a cooling direction (either clockwise or counterclockwise) to draw the external cool air into the electronic devices to have heat exchange with a heat source inside the electronic devices. However, the dust contained in the air may remain inside the electronic devices during the heat exchange. To clean the dust, at the moment the electronic devices are powered-on, the cooling fan usually rotates in a dust-expelling direction (either clockwise or counterclockwise) opposite to the cooling direction for a time period (such as 5 sec) in order to exhaust the accumulated dust from the electronic devices. After the dust exhaustion is finished, the cooling fan rotates in the cooling direction for heat dissipation of the electronic devices.
FIG. 1 shows a conventional rotation direction control circuit 9 that controls forward and reversed rotations of a fan for dust exhaustion and heat dissipation, respectively. The rotation direction control circuit 9 comprises a driving unit 91 and a rotation direction control unit 92, both connected to a power supply VCC. The driving unit 91 is electrically connected to the rotation direction control unit 92. In addition, the driving unit 91 is electrically connected to a motor 8.
With the rotation direction control circuit 9, the rotation direction control unit 92 sends a first rotation control signal to the driving unit 91 during a cooling operation so that the driving unit 91 controls the motor 8 to rotate in the cooling direction for heat exchange. On the contrary, the rotation direction control unit 92 sends a second rotation control signal to the driving unit 91 during a dust-expelling operation so that the driving unit 91 controls the motor 8 to rotate in the dust dispelling direction for dust exhaustion.
However, the conventional rotation direction control circuit 9 generally has some drawbacks. For example, the rotation direction control unit 92 switches between the first and second rotation control signals only at a specific moment. Specifically, at the moment the cooling fan starts, the cooling fan can temporarily rotate in the dust dispelling direction to clean the dust before or after it rotates in the cooling direction for heat exchange. In this operation mechanism, the rotation direction control unit 92 might switch to output the second rotation control signal at an improper moment. In other words, the rotation direction control unit 92 may switch from the first rotation control signal to the second rotation control signal when the scheduled cooling period expires at a moment when heat dissipation still needs to be carried on. Thus, the motor 8 no longer operates to cool down the electronic devices, causing the electronic devices to be more likely damaged.
Furthermore, Taiwanese Patent Number I308678 discloses another conventional rotation direction control method which, when a computer calls for parameters of an interrupt interface of a Basic Input/Output System (BIOS) upon receipt of a command instructing the computer to perform a shutdown operation, detects a temperature of an electronic device in the computer and determines whether the detected temperature is higher than a predetermined temperature. If the detected temperature is higher than the predetermined temperature, a cooling fan is driven to rotate in an opposite direction for dust exhaustion. However, the cooling fan rotates in the opposite direction for dust exhaustion rather than heat dissipation. Therefore, if the conventional rotation direction control method is applied to the computer; which is being operated under a normal operation rather than the shutdown operation where only the parameters of the interrupt interface are called, damages to the electronic device could result as the cooling fan is switched over to rotate in the opposite direction for dust exhaustion when the cooling operation of the electronic device is still highly needed.
In light of the problem, it is desired to improve the conventional rotation direction control method and the conventional rotation direction control circuit 9.